1. Field of the Invention
The present invention relates to a device for supplying fuel to a diaphragm-type carburetor, and particularly, to an improvement in a device for supplying fuel to a diaphragm-type carburetor which includes a constant-pressure fuel chamber which communicates at its outlet bore with a lower end of a fuel nozzle through a fuel jet and a check valve, a fuel pump operated in response to a pulsation pressure in a pulsation pressure generating source to feed the fuel to the constant-pressure fuel chamber, and a fuel-introduction control valve for controlling the introduction of the fuel to the constant-pressure fuel chamber by opening and closing an inlet bore in the constant-pressure fuel chamber, wherein a fuel supply passage leading to a fuel tank is connected to an intake side of the fuel pump.
2. Description of the Related Art
The above diaphragm-type carburetor is already known, as disclosed in, for example, Japanese Patent Application Laid-open No.10-131807.
In the diaphragm-type carburetor as described above, a large amount of fuel vapor may be often generated from the fuel fed from the fuel pump toward the constant-pressure fuel chamber during operation of the engine for a long period of time. If the large amount of fuel vapor is ejected at once from the fuel nozzle, the air-fuel ratio of an air-fuel mixture is extremely reduced, thereby causing a disorder in the operation of the engine.
The present inventors have cleared that the cause of generation of a large amount of fuel vapor from the fuel fed from the fuel pump toward the constant-pressure fuel chamber resides in that there is a very large difference in temperature between the diaphragm-type carburetor mounted to the engine and the fuel pumped from the fuel tank to the fuel pump of the carburetor. More specifically, a diaphragm-type carburetor is generally mounted to an engine through an insulator, but the operation of the engine for a long period of time causes the heat generated in the engine to be gradually propagated to the carburetor through the insulator to heat the carburetor. Therefore, if the fuel having a relatively low temperature is introduced from the fuel tank into the carburetor heated to a relatively high temperature, the fuel is heated rapidly, whereby bubbles included in the fuel are expanded suddenly to generate a large amount of fuel vapor.